Recently, nucleoprotein complexes containing viral DNA have been extracted from cells infected with the oncogenic papovaviruses, polyoma and SV40. In addition, similar complexes were isolated from the core of purified mature virions. The proteins of these viral DNA-protein complexes have been identified as host cell histones. Histones are thought to be important in maintaining a condensed, supercoiled configuration in cellular DNA, as well as contributing to transcriptional control. The similarities of viral and cellular nucleohistones suggest that similar mechanisms might affect the structure and expression of papovavirus DNA. Consequently, the purpose of this investigation is to determine the contribution of histones to the structure and expression of viral DNA in lytically infected and transformed cells. The project is designed to answer three basic questions concerning the role of histones in control of papovavirus DNA structure and expression: 1) Does histone contribute to the formation of superhelical structure in viral DNA? 2) Does histone control the patterns of transcription of the viral genome? 3) Does histone participate in viral DNA synthesis?